Recirculating combustor

ABSTRACT

Combustor structure particularly adapted for supplying motive fluid to a gas turbine engine or the like. A combustion liner is mounted within an inner casing, the two defining between them a recirculation duct for combustion products. The inner casing is mounted within an outer casing, these two defining between them a dilution air duct in which the dilution air is heated while cooling the recirculating combustion products. The combustion liner wall is double and defines combustion air duct between the walls with a Coanda nozzle at its downstream end which is the nozzle of a jet pump to effect the recirculation. The combustion liner is supported from the forward wall of the casing by tubes which conduct combustion air into the liner. A valve arrangement controls the ratio of combustion air to dilution air.

United States Patent [191 Stettler et al. July 10, 1973 RECIRCULATINGCOMBUSTOR Primary Examiner-William F. ODea 75 Inventors: Richard J.Stettler; Albert J. Fergus Verdouw, both of Indianapolis, Ind. Attorneypaul F'tzpamck et [73] Assignee: General Motors Corporation,

Detroit, Mich. [57] ABSTRACT Fildl .l 1972 Combustor structureparticularly adapted for supplying [2!] Appl NOJ 220,607 motive fluid toa gas turbine engine or the like. A combustion liner [8 mounted withinan inner casing, the two defining between them a recirculation duct forcom- U.S. bustion products The inner casing is mounted 431/l 4131/352 anouter casing, these two defining between them a di- [5 Int. Cl. lutionair duct in the dilution air is heated Field of Search cooling therecirculating combustion products. The 39-52, 39-65 combustion linerwall is double and defines combustion air duct between the walls with aCoanda nozzle at its References Cited downstream end which is the nozzleof a jet pump to UNITED STATES PATENTS effect the recirculation. Thecombustion liner is sup- 2,869,629 1/1959 Nerad 431/351 x P fmm thefOrward Wall 0f the Casing by tubes 3 273 2 9 9 Childree 43 351 X whichconduct combustion air into the liner. A valve 3,306,333 2/1967 Mock60/39.65 arrangement controls the ratio of combustion air to di-3,319,692 5/1967 Reba et al... 431/116 lution air. I 3,656,298 4/1972Wade 60/3952 5 Claims, 13 Drawing Figures I l a g c O O 0 o 5 0 0 o 0 OO 0 o K.) w o? u (.2

U u u s.) O u u 0 U 0 0 O L.) Q 4.) u 0 O O u 0 u u o w UUL') O0 O k) (JC) Q U Q Q o 0 2: L) o o o o o Q 0 G 4-2 0 a c O o Q Q c {Q o a o bPATENTEUJHI. 1 man SHEH k [If 4 RECIRCULATING COMBUSTOR Our invention isdirected to combustion apparatus particularly suited for use with gasturbine engines and in other installations in which combustion productsare generated for use at high temperature.

In the usual gas turbine combustor, air under substantial pressure, andwhich may be relatively hot upon introduction into the combustor, ismixed with fuel and combustion takes place at high temperature in arather small space; in other words, the combustion apparatus may becalled a high-intensity type. Such combustion devices ordinarily have avery low output of unburned hydrocarbons and of carbon monoxide.However, because of the high combustion temperature, there is aconsiderable tendency for oxygen and nitrogen moleclues to becomedissociated and to recombine to form an oxide of nitrogen. These oxidesof nitrogen are regarded as atmospheric pollutants.

It is possible to minimize nitrogen oxide formation by vigorouslyrecirculating inert combustion products into the combustion zone of thecombustion apparatus to reduce the oxygen concentration, and by coolingthe combustion products as they are recirculated to reduce thetemperature level in the combustion zone, by heat exchange with dilutionair. Because of the greater dilution of the oxygen and because of thelower maximum temperature in the combustion zone for a given ultimatetemperature of the motive fluid, the concentration of nitrogen oxide inthe motive fluid which utimately is discharged from the engine is quitesubstantially reduced.

The subject matter of this application is a unitary combustion apparatusor combustor for research into the operation of recirculating combustorsfor improving their characteristics, to provide a further practicalembodiment of these principles of pollutant reduction.

The principal objects of our invention are to provide a practical andefficient high-intensity combustion apparatus having a low output ofundesired exhaust components, particularly nitrogen oxides, to improvethe emission characteristics of gas turbine engines and other continuouscombustion devices, and to provide a superior combustion apparatusincluding means for recirculating combustion products to the combustionzone.

The nature of this invention and its advantages will be more clearlyapparent from the succeeding detailed description of the preferredembodiment of the invention and the accompanying drawings thereof.

FIG. 1 is a view, parallel to its axis, of a combustion apparatus, withparts cut away and in section.

FIG. 2 is an end view of the same taken in the plane indicated by line2- 2 in FIG. I, with parts broken away.

FIG. 3 is a partial cross sectional view taken in the plane indicated byline 33 in FIG. I and with parts broken away.

FIG. 4 is a partial cross sectional view taken on the plane indicated byline 44 in FIG. 1.

FIG. 5 is a partial cross sectional view taken on the plane indicated byline 5-5 in FIG. 1.

FIG. '6 is a fragmentary cross sectional view taken on the planeindicated by line 66 in FIG. 3.

FIG. 7 is a fragmentary cross sectional view taken on the planeindicated by line 7-7 in FIG. 1.

FIG. 8 is an enlarged view corresponding to a portion of FIG. 1 taken ina plane containing the axis of the combustion apparatus.

FIGS. 9, l0, and 11 are fragmentary sectional views taken on the planesindicated by line 99, l0-l0, and 11-11, respectively, in FIG. 8.

FIG. 12 is a fragmentary sectional view taken on the plane indicated bythe line 1212 in FIG. 1.

FIG. 13 is a greatly enlarged fragmentary view of a roughened surface.

Before proceeding to the detailed description of the structure shown inthe drawings, we may mention that recirculating combustion devices ofone sort or another for one purpose or another have been proposed.Examples which may be noted are shown in United States patents asfollows: McCollum U.S. Pat. No. 2,517,399, Aug. 1, 1950; Johnson U.S.Pat. No. 2,701,608, Feb. 8, 1955; Reingold et al. U.S. Pat. No.2,716,863, Sept. 6, 1955; Von Linde U.S. Pat. No. 3,174,526, March 23,1965; and Reba et al. U.S. Pat. No. 3,319,692, May 16, 1967.

Referring to FIGS. 1 and 2, a combustion apparatus embodying ourinvention is shown as mounted within a housing or pressure vessel 2 towhich compressed air is supplied for combustion, the compressed airflowing into and filling the space or plenum 3 within the housing. Thehousing may be suitably closed at its upstream end (its left end asillustrated) by means (not shown) through or from which the compressedair is supplied. The combustor or combustion apparatus 4 is a structureprimarily of sheet metal, having a circular cross section, an upstreamend at 5, and a downstream end at 6. At the downstream end thecombustion apparatus terminates in a motive fluid outlet sleeve 7 which,in the installation illustrated, discharges through an opening 8 in anannular plate 10 which closes the downstream end of the housing 2. Inthe usual gas turbine installation, the housing 2 would be supplied withair from the compressor of the engine and the motive fluid outlet 7would be connected to the inlet of a turbine driving the compressor.However, such environmental details are immaterial to a disclosure ofour combustion apparatus.

The combustion apparatus comprises an outer casing 1 l, the majorportion of which is cylindrical, and which tapers toward its downstreamend to a dilution air outlet portion 12 and finally to an end sleeve 14within which the motive fluid outlet 7 is mounted. The outlet end ofcasing 11 is piloted on a ring 15 welded in the opening 8. The principalsupport of the combustor is provided by three radial locating pins 16removably mounted in the housing 2 at spacing about its axis, each ofwhich enters an opening in a boss 18 welded to the outerv casing tolocate the casing axially and center the casing in the housing. Theupstream end of outer casing 11 is slidably fitted over a front plateassembly, the center of which is supported by a fuel nozzle 20 supportedfrom the housing 2 by means not illustrated.

An inner casing 22 is mounted within and rather closely spaced from theouter casing, the inner casing being of generally cylindrical shape andbeing tapered down to a combustion products outlet 23.

Referring to FIG. 12, a zigzag or wavy strip 24, welded or brazed toboth, connects the combustion products outlet 23 to the outlet sleeve 7.Three equally spaced bosses 26 fixed to the downstream end of innercasing 22 provide sockets which receive the inner ends of the locatingpins 16. The outer casing 11 has a ring of dilution air holes 27 at theupstream end and a second ring of dilution air holes 28 downstream fromholes 27. The dilution air so admitted flows through a dilution air duct30 defined between the casings ll and 22. Eight equally spaced spacerstrips 31 (see also FIG. 1 1) fixed to the outer surface of the innercasing and extending axially thereof serve to insure that any distortionof the inner and outer casings does not unduly vary the width of thedilution air duct 30.

A combustion liner 32, within which the major part of the combustionzone is located, is mounted concentrically within the inner casing withits upstream end defined by a toroidal manifold 34 (see also FIG. 8) andwith its downstream end at 35. The combustion liner is a double-walledgenerally cylindrical structure with an outer wall 36 and an inner wall38. There are sixteen spacer strips 39 (FIG. extending axially of andfixed to the inner wall 38 to space it from the outer wall 36. Thecombustion liner double wall defines an annular combustion air duct 40extending from the manifold 34 to an annular jet nozzle 42. The nozzle42 is defined between the donwstream end of wall 38 and the recurveddownstream end portion 43 of wall 36. Sixteen sheet metal spacers 44brazed to the inner and outer walls assure the concentricity of thewalls and the proper width of the nozzle. It may be noted at this pointthat the downstream end portions of the outer and inner walls areseparate physically from the upstream portion, these meeting at lapjoints 46 provided for fabrication purposes at which the parts aretack-welded. The outer wall 36 is welded to manifold 34 (see FIG. 6) andinner wall 38 has a leading edge portion slidably received in a slot ina ring 47 welded to the manifold.

Referring particularly to FIG. 8, it will be seen that the annular jetnozzle 42 discharges the combustion air over the rounded or toroidalsurface of the downstream end 35 of outer wall 36. Because of the Coandaeffect, this air follows surface 35 into a recirculation duct 49 definedbetween wall 36 and inner casing 22. The jetted air entrains combustionproducts flowing out of the downstream end of liner 32 and impels themforwardly through duct 49. The combustion air and recirculatedcombustion products are mixed in duct 49 and cooled to some extent byheat transfer through wall 36 and casing 22. The mixture is introducedinto the upstream end of liner 32, as will be explained. Because of theconsiderable circumference of the liner, the jet pump is of quitesubstantial size and capacity.

Considering now the upstream end of the combustor and more specificallythe front plate assembly 19, the slightly converging upstream end of theinner casing 22 terminates in a radial flange 48. An inner front plate50 abuts flange 48 and is fixed at its center to a ferrule 51 which ispiloted on the fuel nozzle 20. An outer front plate 52 has itsperipheral portion abutting a bolting ring 53. This abuts a secondbolting ring 54. The flange 48 and the margin of inner front plate 50are aligned with rings 53 and 54 by dowels 55. The rings 53 and 54 arefixed together by a ring of cap screws 56. The dowels 54 pass throughradial slots in parts 48 and 50, which are free to expand radiallyrelative to rings 53 and 54. The forward end of the outer casing lll isslidably piloted on the bolting rings 53 and 54.

The center of front plate 52 is mounted on the ferrule 51 and retainedby a nut 58. Front plate 52 (FIG. 4) has an outer ring of sixteenradiating slots 59 and an inner ring of eight smaller slots 60. Theslots 59 and 60 admit combustion air from the plenum 3 to the combustionapparatus. The air entrances are variably throttled by a valve plate 62(FIGS. 1 and 2) having a central ferrule 63 piloted on ferrule 51 androtatable about the axis of the fuel nozzle 20. Valve plate 62 isrotated by a push-pull rod 64 extending through a guiding boss 65 on thehousing 2 and coupled through link 66 to an arm 67 fixed to the valveplate. The margins of the valve plate are held in contact with the outerplate 52 by eight clips 68.

The valve plate 62 has 16 radiating slots 69 which cooperate with theslots 59 in the plate 52 to vary com bustion air flow. Each slot 69includes a notch 70 to make the relation of air flow to valve angularposition more nearly linear; that is, to avoid an abrupt cutoff as thevalve closes. The valve plate 62 also has a ring of openings 71 whichoverlie the slots 68 in plate 52 but are of sufficient angular extentnot to thorttle slots 60. Stops 72 may limit the rotary movement ofvalve plate 62.

FIG. 2 also illustrates an igniter 74 mounted in a boss 75 in thehousing which also is shown (rotated into the plane) in FIG. 1. Theigniter extends into proximity to the fuel nozzle 20 for lighting theflame in the burner. The body of the igniter passes through openings inthe outer and inner casings and is disposed forwardly of the leadingedge of the liner 32 at manifold 34.

The air entering through slots 59 and 60, particularly the latter, aidsin cooling the inner front plate 50. This air flows radially outwardbetween plates 50 and 52. Structure to increase heat transfer from thefront plate shown in FIGS. 1 and 5 includes an intermediate ring 76mounted on the front or outer surface of plate 50 by sheet metal fins 77and '78 brazed or welded to the plates 50 and 76. The fins 78 differfrom the fins 77 in length, since the fins 77 reach out to the greatestdiameter of plate 76 while the fins 78 terminate at 79. The innerdiameter of ring 76 is outside of the slots 60 which are always fullyopen. The fins 77, 78 also stiffen the plate 50.

As previously stated, the combustion liner 32 has its upstream end at atoroidal manifold 34 (FIGS. 1, 3, 6, 8, and 9). The manifold isconnected to the inner front plate 50 by eight air tubes 80 whichsupport the combustion liner and conduct air from the front plateassembly 19 into the combustion air duct 40 through the liner. Themanifold is a fabricated structure or weldment comprising a front ring82 of approximately semicircular cross section between the air tubes 80and which is formed to define stub tubes 83 which are welded at 81 tothe discharge end of the tubes 80. Tubes 80 are welded into openings inthe inner front plate 50. The downstream ends of tubes 80 are flattenedand widened circumferentially to provide smoother transition of flowfrom tubes 80 into manifold The manifold 34 also includes a rear ring 84of approximately quarter circular cross section welded to ring 82 atline 86. The ring 47 into which the inner wall a large number ofrelatively large holes 90 and slots 91 in the rear ring 84.

An inner tube 94 is mounted concentrically within each combustion airtube 80. Each tube 94 is welded to three L-shaped sheet metal supports95 which space it from tube 80 and the front ends of which abut theinner front plate 50. As shown in FIG. 5, one of the supports 95 entersa slot in the intermediate ring 76 and the others are retainedpositively against the face of front plate 50 by clips 96 that are fixedto the front plate and overlie the supports 95. Tubes 94 reduce thehydraulic radius of tubes 80 and thus promote more effective cooling ofthese tubes by the air flowing through them. It is calculated theyreduce the temperature of the wall of tube 80 by about 150F.

The forward face of plate 50, the inner surface of tubes 80, radiallyouter surface of wall 38, and the radially inner surface of wall 36 areartificially roughened to improve heat transfer by promoting turbulentflow of the combustion air over these surfaces. Also, the radially outersurface of inner casing 22 is so roughened to improve heat transfer tothe dilution air flowing through the dilution air duct 30.

Preferably, this roughening is effected by etching the surfaces beforethe sheet metal is formed into the final configuration. In the preferredmode of etching illustrated in FIG. 13, two sets of grooves 98intersecting at right angles and directed approximately 45 to thedirection of air flow define isolated .rectangular projections 99between the grooves. Specifically, the grooves may be about 0.014 inchwide and 0.007 inch deep and be spaced approximately 0.039 inches fromcenter to center of the grooves of each set.

Six equally spaced large dilution air holes 100 extend through theoutlet sleeve 7 to provide for discharge of the dilution air flowingthrough duct 30 into the outlet of the combustion apparatus. Thisdilution air, which has been heated in its passage through duct 30 byheat transfer from the combustion products, mixes with the combustionproducts flowing from the combustion products outlet 23 to provide themotive fluid for the engine with which the combustor is used.

It will be appreciated that the inner wall 38 of the combustion liner isin an extremely hot location and there is considerable heat transferfrom the combustion zone through wall 38 to the combustion air flowingthrough duct 40 to the Coanda nozzle 42.

The tubes 80 are in a less hot location. They are also cooled to someextent by the fresh combustion air entering through these tubes. Themixture of combustion air and recirculated combustion products from duct49 flows through the gaps between these tubes 80. The inner front plate50, which also is exposed to radiation from the flame, is cooled to avery considerable extent by the combustion air flowing between it andthe outer front plate 52.

The operation of the combustor should be clear but may be describedbriefly. In operation, compressed air is fed to the apparatus so as toflow into the plenum 3. Air flows through the slots 59 and 60 in theouter front plate 52. The combustion air flows through tubes 80 into themanifold 34 and thence through the duct 40 defined between the walls ofthe combustion liner 32, out the annular nozzle 42 where, due to theCoanda effect, the air follows the curved rear surface 35 of the outerwall and flows forwardly through the recirculation duct, entraining withit a very substantial part of the combustion products. It iscontemplated, for example, that the recirculated combustion products befrom one to two or more times the mass of the entering combustion air,preferably twice the mass. The mixture of recirculated combustionproducts and added air flows forwardly, being cooled to a considerableextent by heat exchange through inner casing wall 22 to the dilutionair, then flows between tubes into the area adjacent nozzle 20 andrearwardly through the combustion liner 32. Fuel sprayed in the usualconical pattern from nozzle 20 is ignited by the igniter '74, which maybe an electric spark device, and the resulting combustion heats themotive fluid. Actual combustion takes place from near the fuel nozzleabreast of tubes 80 on back through the liner 32. A considerable part ofthe combustion products flow through the outlet 23 into the outletsleeve 7. Dilution air, which enters through holes 27 and 23 into thedilution air passage 30 between the outer and inner casings, flowsrearwardly, being heated by the recirculating combustion products, andfinally entersthe combustor outlet through the holes 100, the stream ofheated air being mixed with the stream of combustion products.

The valve plate 62 makes it possible to vary the admission of combustionair and thereby the ratio of combustion air to dilution air, and thusprovide control of the fuel air ratio in the combustion zone to a veryconsiderable extent. Normally, the ratio of combustion air to dilutionair is lowered at low fuel flow rates.

Variation of the ratio of combustion air to dilution air may also beeffected by suitable means (not illustrated) for controlling flowthrough holes 100. Such control of dilution air may be employed inconjunction with, or instead of, control of primary air entrances.

The recirculation of combustion products and the cooling of recirculatedcombustion products tend to reduce both the concentration of exygen andthe combustion temperature in the combustion zone and thereby theproduction of nitrogen oxides.

The simplicity, effectiveness, and structural strength of the preferredstructure illustrated will be apparent, and the arrangements for coolingthe hotter parts of the combustion liner also contribute to itsdurability. While the combustion apparatus may be built in various sizesand proportions for various installations, it may be pointed out fordisclosure purposes that the particular combustion apparatus illustratedis shown in proportion and that the overall diameter of the outer casing11 is just over eleven inches.

The detailed description of the preferred embodiment of the inventionfor the purpose of explaining the principles thereof is not to beconsidered as limiting or restricting the invention, since manymodifications may be made by the exercise of skill in the art.

As used in the appended claims, the term combustion liner is intended toinclude the ring of tubes 8 and the liner 32, these elements providingthe peripheral boundary of the combustion space.

We claim:

1. Combustion apparatus having an upstream end and a downstream endcomprising, in combination, an outer casing defining inlet means fordilution air adjacent the upstream end; an inner casing mounted withinthe outer casing and defining an outlet at its downstream end forcombustion products; the casings defining between them a duct fordilution air extending from the said inlet means past the said outlet; acombustion liner mounted within the inner casing having an upstreaminlet end adjacent the upstream end of the inner casing and a downstreamoutlet end upstream from the said combustion products outlet; the innercasing and the combustion liner defining between them a recirculationduct for combustion products extending from the downstream end of theliner to the upstream end of the liner; the combustion liner having adouble wall defining within the wall a combustion air duct extendingfrom the upstream to the downstream end of the liner; the combustion airduct having air inlet means at the upstream end and terminating in anannular jet pump nozzle at the downstream end adapted to discharge thecombustion air over the outer wall of the combustion liner into therecirculation duct and to entrain and energize a substantial portion ofthe combustion products flowing from the downstream end of the linerthrough the recirculation duct into the upstream end of the liner; thecombustion liner defining a combustion zone therein; means for injectingfuel into the combustion zone; and means downstream of the said outletfor mixing dilution air flowing from the dilution air duct withcombustion products flowing from the inner casing.

2. Combustion apparatus having an upstream end and a downstream endcomprising, in combination, an outer casing defining inlet means fordilution air adjacent the upstream end; an inner casing mounted withinthe outer casing and defining an outlet at its downstream end forcombustion products; the casings defining between them a duct fordilution air extending from the said inlet means past the said outlet; acombustion liner mounted within the inner casing having an upstreaminlet end adjacent the upstream end of the inner casing and a downstreamoutlet end upstream from the said combustion products outlet; the innercasing and the combustion liner defining between them a recirculationduct for combustion products extending from the downstream end of theliner to the upstream end of the liner; the inner casing having aconfiguration promoting heat transfer between the recirculation duct andthe dilution air duct; the combustion liner having a double walldefining within the wall a combustion air duct extending from theupstream to the downstream end of the liner; the combustion air ducthaving air inlet means at the upstream end and terminating in an annularjet pump nozzle at the downstream end adapted to discharge thecombustion air over the outer wall of the combustion liner into therecirculation duct and to entrain and energize a substantial portion ofthe combustion products flowing from the downstream end of the linerthrough the recirculation duct into the upstream end of the liner; thecombustion liner defining a combustion zone therein; means for injectingfuel into the combustion zone; and means downstream of the said outletfor mixing dilution air flowing from the dilution air duct withcombustion products flowing from the inner casing.

3. Combustion apparatus having an upstream end and a downstream endcomprising, in combination, an outer casing defining inlet means fordilution air adjacent the upstream end; an inner casing mounted withinthe outer casing and defining an outlet at its downstream end forcombustion products; the casings defining between them a duct fordilution air extending from the said inlet means past the said outlet; acombustion liner mounted within the inner casing having an upstreaminlet end downstream of the upstream end of the inner casing and adownstream outlet end upstream from the said combustion products outlet;the inner casing and the combustion liner defining between them arecirculation duct for combustion products extending from the downstreamend of the liner to the upstream end of the liner; the combustion linerhaving a double wall defining within the wall a combustion air ductextending from the upstream to the downstream end of the liner; thecombustion air duct having air inlet means at the upstream end andterminating in an annular jet pump nozzle at the downstream end adaptedto discharge the combustion air over the outer wall of the combustionliner into the recirculation duct and to entrain and energize asubstantial portion of the combustion products flowing from thedownstream end of the liner through the recirculation duct into theupstream end of the liner; the combustion liner defining a combustionzone therein; means for injecting fuel into the combustion zone; meansdownstream of the said outlet for mixing dilution air flowing from thedilution air duct with combustion products flowing from the innercasing; and variable means for controlling the ratio of combustion airto dilution air.

4. Combustion apparatus having an upstream end and a downstream endcomprising, in combination, an outer casing defining a first inlet meansfor dilution air adjacent the upstream end and defining second inletmeans for dilution air intermediate the ends; an inner casing mountedwithin the outer casing and defining an outlet at its downstream end forcombustion products; the casings defining between them a duct fordilution air extending from the upstream end of the casings past thesaid outlet; a combustion liner mounted within the inner casing havingan upstream inlet end adjacent the upstream-end of the inner casing anda downstream outlet end upstream from the said combustion productsoutlet; the inner casing and the combustion liner defining between thema recirculation duct for combustion products extending from thedownstream end of the liner to the upstream end of the liner; the innercasing having a configuration promoting heat transfer between therecirculation duct and the silution air duct; the combustion linerhaving a double wall defining within the wall a combustion air ductextending from the upstream to the downstream end of the liner; thecombustion air duct having air inlet means at the upstream end andterminating in an annular jet pump nozzle at the downstream end adaptedto discharge the combustion air over the outer wall of the combustionliner into the recirculation duct and to entrain and energize asubstantial portion of the combustion products flowing from thedownstream end of the liner through the recirculation duct into theupstream end of the liner; the combustion liner defining a combustionzone therein; means for injecting fuel into the combustion zone; meansdownstream of the said outlet for mixing dilution air flowing from thedilution air duct with combustion products flowing from the innercasing; and variable means for controlling the ratio of combustion airto dilution air.

5. Combustion apparatus having an upstream end and a downstream endcomprising, in combination, an outer casing defining a first inlet meansfor dilution air adjacent the upstream end and defining second inletmeans for dilution air intermediate the ends; and innner casing mountedwithin the outer casing and defining an outlet at its downstream end forcombustion products; the casings defining between them a duct fordilution air extending from the upstream end of the casings past thesaid outlet; a combustion liner mounted within the inner casing havingan upstream inlet end adjacent the upstream end of the inner casing anda downstream outlet end upstream from the said combustion productsoutlet; the inner casing and the combustion liner defining between thema recirculation duct for combustion products extending from thedownstream end of the liner to the upstream end of the liner; the innercasing having a configuration promoting heat transfer between therecirculation duct and the dilution air duct; the combustion linerhaving a double wall defining within the wall a combustion air ductextending from the upstream to the downstream end of the liner; thecombustion air duct having air inlet means at the upstream end andterminating in an annular jet pump nozzle at the downatrem end adaptedto discharge the combustion air over the outer wall of the combustionliner into the recirculation duct and to entrain and energize asubstantial portion of the combustion products flowing from thedownstream end of the liner through the recirculation duct into theupstream end of the liner; the combustion liner defining a combustionzone therein; means for injecting fuel into the combustion zone; meansdownstream of the said outlet for mixing dilution air flowing from thedilution air duct with combustion products flowing from the innercasing; and variable means for controlling the flow of combustion airinto the combustion air duct.

1. Combustion apparatus having an upstream end and a downstream endcomprising, in combination, an outer casing defining inlet means fordilution air adjacent the upstream end; an inner casing mounted withinthe outer casing and defining an outlet at its downstream end forcombustion products; the casings defining between them a duct fordilution air extending from the said inlet means past the said outlet; acombustion liner mounted within the inner casing having an upstreaminlet end adjacent the upstream end of the inner casing and a downstreamoutlet end upstream from the said combustion products outlet; the innercasing and the combustion liner defining between them a recirculationduct for combustion products extending from the downstream end of theliner to the upstream end of the liner; the combustion liner having adouble wall defining within the wall a combustion air duct extendingfrom the upstream to the downstream end of the liner; the combustion airduct having air inlet means at the upstream end and terminating in anannular jet pump nozzle at the downstream end adapted to discharge thecombustion air over the outer wall of the combustion liner into therecirculation duct and to entrain and energize a substantial portion ofthe combustion products flowing from the downstream end of the linerthrough the recirculation duct into the upstream end of the liner; thecombustion liner defining a combustion zone therein; means for injectingfuel into the combustion zone; and means downstream of the said outletfor mixing dilution air flowing from the dilution air duct withcombustion products flowing from the inner casing.
 2. Combustionapparatus having an upstream end and a downstream end comprising, incombination, an outer casing defining inlet means for dilution airadjacent the upstream end; an inner casing mounted within the outercasing and defining an outlet at its downstream end for combustionproducts; the casings defining between them a duct for dilution airextending from the said inlet means past the said outlet; a combustionliner mounted within the inner casing having an upstream inlet endadjacent the upstream end of the inner casing and a downstream outletend upstream from the said combustion products outlet; the inner casingand the combustion liner defining between them a recirculation duct forcombustion products extending from the downstream end of the liner tothe upstream end of the liner; the inner casing having a configurationpromoting heat transfer between the recirculation duct and the dilutionair duct; the combustion liner having a double wall defining within thewall a combustion air duct extending from the upstream to the downstreamend of the liner; the combustion air duct having air inlet means at theupstream end and terminating in an annular jet pump nozzle at thedownstream end adapted to discharge the combustion air over the outerwall of the combustion liner into the recirculation duct and to entrainand energize a substantial portion of the combustion products flowingfrom the downstream end of the liner through the recirculation duct intothe upstream end of the liner; the combustion liner defining acombustion zone therein; means for injecting fuel into the combustionzone; and means downstream of the said outlet for mixing dilution airflowing from the dilution air duct with combustion products flowing fromthe inner casing.
 3. Combustion apparatus having an upstream end and adownstream end comprising, in combination, an outer casing defininginlet means for dilution air adjacent the upstream end; an inner casingmounted within the outer casing and defining an outlet at its downstreamend for combustion products; the casings defining between them a ductfor dilution air extending from the said inlet means past the saidoutlet; a combustion liner mounted within the inner casing having anupstream inlet end downstream of the upstream end of the inner casingand a downstream outlet end upstream from the said combustion productsoutlet; the inner casing and the combustion liner defining between thema recirculation duct for combustion products extending from thedownstream end of the liner to the upstream end of the liner; thecombustion liner having a double wall defining within the wall acombustion air duct extending from the upstream to the downstream end ofthe liner; the combustion air duct having air inlet means at theupstream end and terminating in an annular jet pump nozzle at thedownstream end adapted to discharge the combustion air over the outerwall of the combustion liner into the recirculation duct and to entrainand energize a substantial portion of the combustion products flowingfrom the downstream end of the liner through the recirculation duct intothe upstream end of the liner; the combustion liner defining acombustion zone therein; means for injecting fuel into the combustionzone; means downstream of the said outlet for mixing dilution airflowing from the dilution air duct with combustion products flowing fromthe inner casing; and variable means for controlling the ratio ofcombustion air to dilution air.
 4. Combustion apparatus having anupstream end and a downstream end comprising, in combination, an outercasing defining a first inlet means for dilution air adjacent theupstream end and defining second inlet means for dilution airintermediate the ends; an inner casing mounted within the outer casingand defining an outlet at its downstream end for combustion products;the casings defining between them a duct for dilution air extending fromthe upstream end of the casings past the said outlet; a combustion linermounted within the inner casing having an upstream inlet end adjacentthe upstream end of the inner casing and a downstream outlet endupstream from the said combustion products outlet; the inner casing andthe combustion liner defining between them a recirculation duct forcombustion products extending from the downstream end of the liner tothe uPstream end of the liner; the inner casing having a configurationpromoting heat transfer between the recirculation duct and the silutionair duct; the combustion liner having a double wall defining within thewall a combustion air duct extending from the upstream to the downstreamend of the liner; the combustion air duct having air inlet means at theupstream end and terminating in an annular jet pump nozzle at thedownstream end adapted to discharge the combustion air over the outerwall of the combustion liner into the recirculation duct and to entrainand energize a substantial portion of the combustion products flowingfrom the downstream end of the liner through the recirculation duct intothe upstream end of the liner; the combustion liner defining acombustion zone therein; means for injecting fuel into the combustionzone; means downstream of the said outlet for mixing dilution airflowing from the dilution air duct with combustion products flowing fromthe inner casing; and variable means for controlling the ratio ofcombustion air to dilution air.
 5. Combustion apparatus having anupstream end and a downstream end comprising, in combination, an outercasing defining a first inlet means for dilution air adjacent theupstream end and defining second inlet means for dilution airintermediate the ends; and inner casing mounted within the outer casingand defining an outlet at its downstream end for combustion products;the casings defining between them a duct for dilution air extending fromthe upstream end of the casings past the said outlet; a combustion linermounted within the inner casing having an upstream inlet end adjacentthe upstream end of the inner casing and a downstream outlet endupstream from the said combustion products outlet; the inner casing andthe combustion liner defining between them a recirculation duct forcombustion products extending from the downstream end of the liner tothe upstream end of the liner; the inner casing having a configurationpromoting heat transfer between the recirculation duct and the dilutionair duct; the combustion liner having a double wall defining within thewall a combustion air duct extending from the upstream to the downstreamend of the liner; the combustion air duct having air inlet means at theupstream end and terminating in an annular jet pump nozzle at thedownstream end adapted to discharge the combustion air over the outerwall of the combustion liner into the recirculation duct and to entrainand energize a substantial portion of the combustion products flowingfrom the downstream end of the liner through the recirculation duct intothe upstream end of the liner; the combustion liner defining acombustion zone therein; means for injecting fuel into the combustionzone; means downstream of the said outlet for mixing dilution airflowing from the dilution air duct with combustion products flowing fromthe inner casing; and variable means for controlling the flow ofcombustion air into the combustion air duct.